Bindings of this kind are known, and they normally incorporate a base mounted on the sliding instrument and a boot position-retention device, which is mobile in relation to this base between a boot-retention and a boot-release position. This position-retention device is elastically returned to its position-retention position, normally by a compression spring which generates a return force that intensifies as the position-retention device moves away from its retention position, i.e., a force incorporating the intensity of the stress to which the boot subjects the boot-retention device.
When the stress exerted by the boot exceeds the maximum return force which the spring can transmit to the retention device, the boot is released. This maximum return force is ordinarily termed the "release threshold."
More specifically, the invention concerns safety bindings whose release threshold varies as a function of the speed and length of the stress. Thus, the release threshold is higher for a violent stress than for a mild one. It is known, in fact, that a skier's leg can withstand without damage a strong, brief stress. On the other hand, a stress of low intensity, but of long duration, may prove dangerous.
A device of this type is described, for example, in French Patent No. 2 610 841. This patent describes a damping device which functions in parallel on the spring, so as to generate an additional return force in the event of a violent stress.
The special feature of this patent lies in the fact that the additional return force is limited to a specified value in the event of a very violent stress, e.g., a shock.
The device described in this patent yields good results, but its construction is somewhat complex and bulky. In fact, it requires a hydraulic damping device, a jointed rocker which connects the damping device and one end of the spring, and a rocker-retention stop.